1. Field of the Invention
This invention relates to a surface treatment method for aluminum or an aluminum alloy, and pistons surface-treated thereby, as well as a surface-treating film for aluminum or an aluminum alloy, and sliding members having a sliding surface coated therewith.
More particularly, this invention relates to a surface treatment method which requires simple equipment, can reduce treatment costs, and can yield aluminum or an aluminum alloy having excellent abrasion resistance, corrosion resistance and other properties, as well as pistons having undergone a surface treatment according to this method. It also relates to a surface-treating film suitable for use on the sliding surfaces of internal combustion engines and having excellent abrasion resistance, initial fitness, oil retention and other properties, and sliding members coated with such a slide film.
2. Description of the Related Art
The Alumite treatment which has conventionally been employed is a method for anodizing aluminum in an acid bath to form a hard aluminum oxide film on the aluminum surface. However, this method has the disadvantage that it requires equipment for electric power supply and that it involves a considerable cost because of a slow rate of film formation.
On the other hand, the skirt of an aluminum or aluminum alloy piston as an internal combustion engine component is plated with tin. Although the deposited tin film is effective in bring about good initial fitness, it cannot be expected to have the effect of improving abrasion resistance.